Water, bubble collapse and syngas species in the synthesis of graphene and its derivatives

ABSTRACT

Hydrodynamic cavitation-inducing inertial, non-inertial, and combination reactors are employed in the hydrothermal synthesis of graphene and its derivatives, both in solution and vapor. Various hydrodynamic cavitation reactor embodiments are revealed. Water is used to both nucleate and “self-heal” graphene sheet growth in solution and vapor. Various methods of combustion, hydrothermal and dehydration synthesis of graphene and its derivatives are revealed. Additionally, water and ice are used as a substrate, both alone and in combination with other substrates, to grow and recover useful graphene and its derivatives.

REFERENCE TO RELATED APPLICATIONS

This application is a nonprovisional application of U.S. Provisional Application No. 61/938,119, filed Feb. 10, 2014, entitled “WATER, CAVITATION BUBBLES, AND NASCENT GASES IN THE SYNTHESIS OF GRAPHENE AND ITS DERIVATIVES”; and a continuation-in-part application of U.S. patent application Ser. No. 14/264,360, filed Apr. 29, 2014, entitled “FACILE SYNTHESIS OF GRAPHENE, GRAPHENE DERIVATIVES AND ABRASIVE NANOPARTICLES AND THEIR VARIOUS USES, INCLUDING AS TRIBOLOGICALLY-BENEFICIAL LUBRICANT ADDITIVES”, which is a continuation of U.S. patent application Ser. No. 13/583,507, filed Sep. 7, 2012, entitled “FACILE SYNTHESIS OF GRAPHENE, GRAPHENE DERIVATIVES AND ABRASIVE NANOPARTICLES AND THEIR VARIOUS USES, INCLUDING AS TRIBOLOGICALLY-BENEFICIAL LUBRICANT ADDITIVES”, now U.S. Pat. No. 8,865,113, which is a national phase of PCT Application Number PCT/US12/29276, filed Mar. 15, 2012, entitled “FACILE SYNTHESIS OF GRAPHENE, GRAPHENE DERIVATIVES AND ABRASIVE NANOPARTICLES AND THEIR VARIOUS USES, INCLUDING AS TRIBOLOGICALLY-BENEFICIAL LUBRICANT ADDITIVES”, which is a nonprovisional application of U.S. Provisional Application No. 61/538,528, filed Sep. 23, 2011, entitled “LUBRICATING ADDITIVES, POLISHING COMPOSITIONS, NANOPARTICLES, AND TRIBOLOGICAL COATINGS, AND USES THEREOF, AND METHODS OF NANOPARTICLE, GRAPHENE, AND GRAPHENE OXIDE SYNTHESIS”, U.S. Provisional Application No. 61/541,637, filed Sep. 30, 2011, entitled “LUBRICATING ADDITIVES, POLISHING COMPOSITIONS, NANOPARTICLES, AND TRIBOLOGICAL COATINGS, AND USES THEREOF, AND METHODS OF NANOPARTICLE, GRAPHENE, AND GRAPHENE OXIDE SYNTHESIS”, U.S. Provisional Application No. 61/546,368, filed Oct. 12, 2011, entitled “COMBUSTION SYNTHESIS OF GRAPHENE OXIDE AND GRAPHENE”, U.S. Provisional Patent Application No. 61/568,957, filed Dec. 9, 2011 and entitled “SYNTHESIS OF GRAPHENE, GRAPHENE DERIVATIVES, CARBON-ENCAPSULATED METALLIC NANOPARTICLES, AND NANO-STEEL, AND THE USE OF SEQUESTERED CARBONACEOUS WASTES AND GREENHOUSE GASSES IN SUCH SYNTHESIS METHODS”, U.S. Provisional Patent Application No. 61/579,993, filed Dec. 23, 2011 and entitled “GRAPHENE AND GRAPHENE DERIVATIVES SYNTHESIS BY DEHYDRATION OR PYROLYSIS OF CARBONACEOUS MATERIALS, VAPOR EXFOLIATION OR PAH FORMATION, AND SUBSEQUENT HYDROPHOBIC SELF-ASSEMBLY, U.S. Provisional Patent Application No. 61/596,936, filed Feb. 9, 2012 and entitled “TRIBOLOGICALLY BENEFICIAL CARBONACEOUS MATERIALS AND NANO-ABRASIVE LUBRICANT MOLECULES FROM INTENTIONAL IN-SITU PYROLYSIS OF SACRIFICIAL CYCLIC CARBON CONSTITUENTS. This application is further a continuation-in-part of PCT Patent Application Number PCT/US14/46755, filed Jul. 15, 2014, entitled “PROCESS FOR THE SYNTHESIS OF GRAPHENE AND GRAPHENE DERIVATIVES FROM SO-CALLED GREENHOUSE GASSES AND OTHER CARBONACEOUS WASTE PRODUCTS, which is a nonprovisional application of U.S. Provisional Patent Application No. 61/847,351 entitled “PROCESS FOR THE SYNTHESIS OF GRAPHENE AND GRAPHENE DERIVATIVES FROM SO-CALLED GREENHOUSE GASES AND OTHER CARBONACEOUS WASTE GASES,” filed Jul. 17, 2013. The aforementioned applications are hereby incorporated herein by reference.

BACKGROUND OF THE INVENTION

Field of the Invention

The invention pertains to the field of graphene, graphene oxide, and graphene derivative “bottom-up” molecular synthesis by pyrolysis of hydrocarbon precursor gasses. More specifically, the invention pertains to the use of hydrodynamic cavitation bubble collapse, ultrasonically-induced cavitation bubble collapse, hydrothermal bubble implosion, boiling, refluxing, rapid dehydration, combustion, near-combustion pyrolysis of carbonaceous precursors to produce so-called “syngas” (synthesis gas) species that include carbon monoxide, nascent hydrogen ions and ionic methane precursor gases, for use in the synthesis of graphene, graphene oxide and certain useful graphene derivatives. With respect to use of methods of induced cavitation bubble collapse, the atmospheric conditions inherent in collapsing water bubbles are employed to provide a cost-effective and safe means for syngas species generation (including nascent hydrogen ions and water self-ionization species) and resulting formation of graphitic molecular structures. Additionally, the use of both liquid and frozen water (ice) as a non-metallic substrate for the deposition or epitaxial growth of graphene, graphene oxide and other graphene derivatives, either alone or in combination with other conventional substrates, is revealed.

Description of Related Art

Graphene is a flat, planar, 2-dimensional allotrope of carbon. The carbon atoms of graphene form a hexagonal matrix (chickenwire pattern) of exceptional strength and other physical/electrical properties. Due to graphene's exceptional properties, it is considered a “wonder-material” suitable for replacing many other materials in numerous devices and applications. From a tribological standpoint, graphene, and its “SGAN” (surface-graphitized abrasive nanoparticle) derivatives hold great promise for permanent friction reduction in mechanical systems.

Vapor Deposition Graphene Synthesis in the Current Art

Since graphene's discovery, much effort has been dedicated to designing methods to produce large-area graphene sheet growth. The growth of large-area graphene appears to require so-called “bottom-up” synthesis approaches, where graphene is synthesized from carbonaceous precursor; this in contrast to so-called “top-down” synthesis approaches, whereby already graphitic materials such as graphite or HOPG are exfoliated into small individual graphene scales. Many different methods exist for the bottom-up synthesis of graphene, the majority of which employ common quartz tube furnaces for chemical vapor deposition (CVD) of graphene via epitaxial growth by carbon radical diffusion through metallic substrates. Current CVD methods are universally plagued by relative low efficiency (<15%) (see O′Brian, M. and Nichols, B., “CVD Synthesis and Characterization of Graphene Thin Films,” Army Research Laboratory, ARL-TR-5047, January 2010).

Recently, researchers have experimented with a number of different variations on traditional CVD techniques. Atmospheric Pressure CVD (APCVD) techniques using pyrolized diluted methane gas and hydrogen gas have successfully produced high-quality graphene epitaxially grown on traditional copper foil substrate (See Trinsoutrot et al., “High quality grapheme synthesized by atmospheric pressure CVD on copper foil,” OATAO, Oct. 20-26, 2014). Other CVD methods involve the use of various induced hot plasma events (plasma enhanced CVD or PECVD) to “crack” methane gas into its ionic gaseous constituents necessary for synthesis of graphene and its derivatives (See Woehrl, et al., “Plasma-enhanced chemical vapor deposition of graphene on copper substrates,” AIP Adv., Vol. 4, 2014; Bo et al., “Plasma-enhanced chemical vapor deposition synthesis of vertically oriented graphene nanosheets,” Nanoscale, Vol. 5, Issue 12, pp. 5180-5204, 2013; Kim et al., “Methane as an effective hydrogen source for single-layer graphene synthesis on Cu foil by plasma enhanced chemical vapor deposition,” Nanoscale, Vol. 5, Issue 3, Feb. 7, 2013; Vlassiouk, et al., “Role of hydrogen in chemical vapor deposition growth of large single-crystal graphene,”ACS Nano, Vol. 5, Issue 7, pp. 6069-6076, June, 2011.

Besides the value of nascent hydrogen species produced during the pyrolysis of methane and other carbonaceous feedstocks in the CVD synthesis of graphene, it also has recently elucidated value as a reducing agent for graphene oxide (GO) (See Pham, et al., “Chemical reduction of an aqueous suspension of grpahene oxide by nascent hydrogen,” J. Mater. Chem., Vol. 22, pp. 10530-10536, 2012.

A notable exception to the great majority of usual CVD (methane “cracking”) methods of the current art is the use of commonly-available carbonaceous materials to produce the necessary precursors of methane instead of cracking existing methane gas into its constituents (See Ruan, et al., “Growth of Graphene from Food, Insects, and Waste,” ACS Nano, Vol. 5, Issue 9, pp. 7601-7607, Jun. 29, 2011. Although a step in the correct direction, even this cockroach leg, dog excrement-using approach falls short of the innovations of embodiments of the current invention, in that Ruan et al., still employ a traditional quartz tube furnace to pyrolyze the feedstocks into the necessary nascent hydrogen and syngas species for graphene synthesis. In using boiling methods of the present invention, the necessary syngas species are easily and safely produced at overall temperatures far below those necessary in a tube furnace, as the necessary methane precursor gases are produced before becoming methane, eliminating the need to expend the additional energy to “crack” existing methane gas.

Current Hydrothermal (Wet) Synthesis of Graphene

The use of various hydrothermal synthesis techniques for the “wet” production of nanoparticles and molecules is known to the art (see, for example, Lester, E. et al, “Controlled continuous hydrothermal synthesis of cobalt oxide (Co3O4) nanoparticles,” Progress in Crystal Growth and Characterization of Materials, Vol. 58(1), March 2012, pp. 3-13; Wang, Q. et al., “Synthesis of ultrafine layered double hydroxide (ldhs) nanoplates using a continuous-flow hydrothermal reactor,” Nanoscale, Issue 1, 2013, pp. 114-117; Lester, E. et al., “Impact of reactor geometry on continuous hydrothermal synthesis mixing,” Materials Research Innovations, Vol. 14(1), 2010, pp. 1703-1710; Cabañas, A and Poliakov, M., “The continuous hydrothermal synthesis of nano-particulate ferrites in near critical and supercritical water,” J. of Mater. Chem., March 2001, and Aimable, A. et al., “Continuous hydrothermal synthesis of inorganic nanopowders in supercritical water: Towards a better control of the process,” Powder Technology, Vol. 190(1-2), March 2009, pp. 99-106). Further, supercritical water and its self-ionization products are known to the art to assist in the nucleation of nanoparticles in solution (see Lester et al., “Reactions Engineering: The supercritical water hydrothermal synthesis of nano-particles,” and Ahn et al., “Self-assembled foam-like graphene networks formed through nucleate boiling,” Sci. Rep., 2013). With hydrothermal synthesis methods, the morphology, composition and size of resulting nano-particles can be easily manipulated and controlled by adjusting the experimental parameters, such as the particular choice of alcohol as the solvent (see Gotić, M. and Svetozar, M., “Synthesis of nanocrystalline iron oxide particles by the esterification reaction in the iron(III) oxide/acetate/alcohol system,” E-MRS (European Materials Research Society, Strasbourg, France) Fall Meeting, Symposium A, 2007 (Oral Presentation), Warsaw University of Technology, Warsaw, Poland; Ivanda et al., “XRD, Raman and FT-IR spectroscopic observations of nanosized TiO2 synthesized by the sol-gel method based on an esterification reaction,” J. Mol. Struct., Vol. 481, 1999, pp. 645-649; Gotić et al., “Influence of synthesis procedure on the morphology of bismuth oxide particles,” Mat. Lett., Vol. 61, 2007, pp. 709-714).

U.S. Provisional Patent Application Ser. No. 61/538,528 by Shankman, supra, discloses a method of hydrothermal reflux (boiling) synthesis of graphene and its derivatives from sugar dissolved in a solvent; in one cited embodiment, the solvent formulation comprises water, isopropanol or ethanol and USP white mineral oil. The resulting synthesized (PAH/graphene scale-rich) pyrolysis vapors are either directed to a suitable substrate or alternatively channeled to a “hydrophobic self-assembly” pool of water for formation of large-area graphene sheets at the water's surface. See also U.S. Pat. No. 8,865,113 to Shankman and titled FACILE SYNTHESIS OF GRAPHENE, GRAPHENE DERIVATIVES AND ABRASIVE NANOPARTICLES AND THEIR VARIOUS USES, INCLUDING AS TRIBOLOGICALLY-BENEFICIAL LUBRICANT ADDITIVES.

Recently, unaffiliated researchers independently confirmed the ability to hydrothermally synthesize graphene oxide (GO) sheets using a pyrolized sugar-water solution contained in an autoclave apparatus. These researchers described the GO sheet formation on the solution surface (within the sealed autoclave) as resulting from “cyclic polymerization” (see Tang et al., “Bottom-up synthesis of large-scale graphene oxide nanosheets,” J. Mater. Chem., Vol. 22, 2012, pp. 5676-5683). Hydrothermal synthesis of graphene (quantum dots) from sugar-water solutions has also been recently reported by use of microwave irradiation (see Tang et al., “Deep Ultraviolet Photoluminescence of Water-Soluble Self-Passivated Graphene Quantum Dots,” ACS Nano., Vol. 6 (6), 2012, pp. 5102-5110).

The Shankman methods described infra reveal the suitability of numerous carbonaceous feedstocks for hydrothermal (reflux) pyrolysis (or oxidation/reduction) into graphene and its derivatives. In July of 2012, unrelated researchers confirmed that premise by reportedly synthesizing graphene sheets from the reflux of carbonaceous tetrachloroethylene (PERC) and raw sodium metal (as the reducing agent), using a light paraffin oil as the solvent (see Wang et al., “Facile Preparation of Carbon Nanotubes and Graphene Sheets by a Catalyst-Free Reflux Approach,” Nano. Res., July, 2012). Previous to the Wang et al. study, unaffiliated researchers at the University of Idaho (Moscow, Id., U.S.A.) likewise confirmed the synthesis of graphene sheets from the “fumes” of pyrolyzed roofing tar (see Cheng et al., “Synthesis of graphene paper from pyrolyzed asphalt,” Carbon, Vol. 49 (8), July 2011, pp. 2852-2861). The Cheng et al. team heated asphalt (known to contain numerous VOCs, aromatics, polyaromatics and alicyclics) to its decomposition point in a covered (but open to the atmosphere) ceramic crucible, noticing resulting deposition of graphene on the underside of a quartz boat within the unsealed oven. Unfortunately, much of the resulting nascent vapors were allowed to escape the Cheng oven apparatus unused.

In an example of recent oxidative synthesis involving a strong oxidizer in solution, GO was reacted with urea and ammonium nitrate and heated to 250° C. for 2 hours to produce graphene. Although the researchers reported the production of “vapors” during the reaction, those vapors were vented to the atmosphere unused as waste (see Kishore et al., “Combustion Synthesis of Graphene and Ultracapacitor Performance,” 2013 G E Global Research, Niskayuna, N.Y., U.S.A.; also published as Kishore et al., “Combustion Synthesis of Graphene and Ultracapacitor Performance,” Bull. Mater. Sci. Vol. 36, No. 4, August 2013, pp. 667-672). Similarly, other researchers recently reacted sugar (glucose) and ammonium chloride to produce (self-named) so-called “Strutted Graphene” (in reality, graphitic foam and its residual Maillard reaction intermediate—melanoidin) via so-called “sugar-blowing” (in reality, sugar dehydration a/k/a dehydration/oxidative synthesis of graphene previously described by Shankman) that was subsequently annealed to improve its graphitic quality by conversion/carbonization of the remaining residual melanoidin to graphene. In this example, the molten sugar syrup precursor solution was slowly oxidized (rather than rapidly oxidized to produce a PAH-rich vapor stream to be collected and used in a self-assembly pool), resulting in the trapping of certain reaction gases in the growing graphitic foam matrix; this causing the formation of the internal bubble cavities found therein. Although this Wang et al. process produces graphitic foam-like material, it does not yield (commercially-useful) large-area sheets of 2-D graphene films (see Wang et al., “Three-dimensional strutted graphene grown by substrate-free sugar blowing for high-power-density supercapacitors,” Nature Comm., Vol. 4, Article No. 2905, Dec. 16, 2013).

In the present invention, the carbon radical/PAH/graphene scale-containing vapors are intentionally collected and separated from the reactants in solution, then subsequently purposefully directed to either a substrate or to a hydrophobic self-assembly pool for the production of large-area graphene sheets, apart from the dirty reactant-containing solvents of their synthesis reaction. Additionally, hydrothermal liquid cavitation reactors are employed for the synthesis of graphene and its derivatives. The use of “cavitation synthesis” capitalizes on the unique energy of collapsing vacuum cavitation bubbles to provide the necessary “locally pyrolytic synthesis conditions” (LPSC or LPS) necessary for graphene synthesis, without the need for extreme systemic temperatures or pressures found in the related technologies of the current state of the art.

Other Use of Water in Molecular Synthesis

Water, the most abundant substance on the planet, remains one of the most hotly debated and largely misunderstood compounds in nature (see generally, the work of Schauberger, V. (1885-1958, Linz, Austria), Schauberger, W. (Viktor's son, PKS Institute, Bad Ischl, Austria), Rachmanin, Y. A. and Kondratrov, V. K. (Russian Academy of Natural Sciences, Moscow, Russia), Emoto, M. (Tokyo, Japan; The Secret Life of Water, © 2005 Simon & Schuster, UK Ltd., London, U.K.; Messages from Water and the Universe, © 2010 Hay House, Inc., Carlsbad, Calif., U.S.A.), Grander, J., (1930-2012, Jochberg, Austria; Johann Grander: Der Wassermann von Tirol, © 2003 Uranus Verlagsgesellschaft m.b.H., Vienna, Austria, Film).

Russian researchers Yuri Rachmanin and Vladimir Kondratov (supra) have suggested that their studies of vertical “ice-like” hexagonal crystals in liquid water reveal that such crystals may impart transmitted electromagnetic energy (from the Earth's gravitational fields) to nearby water molecules in solution via a “donor/acceptor” energy-transfer relationship. This transmission of electromechanical energy by water may be part of its demonstrated “self-healing” and “hydrophobic self-assembly” nature with respect to forming graphene using the methods of the current invention.

Current trends in the state of the art and the work of Shankman, R. infra appear to reveal and confirm the relationship between water's unique and special properties and its place in the synthesis of graphene. It is postulated in embodiments of the current invention that water can form clathrate cages (clathrate hydrates) around carbon atoms and molecules in solution to facilitate the assembly of graphitic networks of hexagons, acting as a template and charge-transfer agent during assembly of the matrices (See generally, E. Dendy Sloan, Jr. and Carolyn Koh, Clathrate Hydrates of Natural Gages, Third Edition, © 2007, CRC Press, Boca Raton, Fla., U.S.A.; see also (somewhat illustratively), Patrice Mélinon (2011), SiC Cage Like Based Materials, Silicon Carbide—Materials, Processing and Applications in Electronic Devices, Dr. Mournita Mukherjee (Ed.), ISBN: 978-953-307-968-4, InTech, Available from: http://www.intechopen.com/books/silicon-carbide-materials-processing-and-applications-in-electronicdevices/sic-cage-like-based-materials; Zhu et al., “Encapsulation kinetics and dynamics of carbon monoxide in clathrate hydrate,” Nat. Comm., Vol. 5, Art. Num. 4128, Jun. 17, 2014; Koh, et al., “Reactive radical cation transfer in the cages of icy clathrate hydrates,” Korean J. Chem. Eng., Vol. 32, Issue 2, pp. 350-353, 2014.

The current state of the art in hydrothermal nucleate boiling molecular synthesis appears to be limited to mere liquid perturbation mixing by simple use of colliding opposing streams; so-called “counter-current mixing” (see U.S. Pat. No. 7,556,436 B2 to Lester, E. et al.). However, the use of cavitation bubbles in the physical and chemical molecular transformations of compounds has been known to the art for some time (see Gogate, et al., “Cavitation Reactors: Efficiency Assessment Using a Model Reaction,” AlChE J., Vol. 47(11), November 2001, pp. 2526-2538; Grogate, P. R. and Pandit, A. B., “Engineering design methods for cavitation reactors II: Hydrodynamic cavitation,” AlChE J., Vol. 46(8), August 2000, pp. 1641-1649). The postulated use, however, of the power of cavitation bubbles for LPSC/LPS of graphene and its derivatives (other than by Shankman, R. infra), remains unreported.

Dehydration Synthesis of Graphene

Dehydration synthesis via an essentially intumescent (flameless) reaction occurs when an oxidizer chemically attacks the surface of a solid carbonaceous fuel. U.S. Provisional Patent Application Ser. No. 61/538,528 by Shankman, supra, discloses (among others) a dehydration/intumescent method of acid dehydration of sugar to produce graphene-rich vapors. This particular sugar-dehydration embodiment involves the use of sulfuric acid (commonly found in drain cleaner) to dehydrate a saturated sugar solution to produce graphitic carbon species. Unfortunately, if sufficient time is not provided for the resulting vapors to interact with water, the product (although layered) will only be partially graphitic in nature; owing to insufficient “self-healing” time to form a perfect network of hexagons. Embodiments of the present invention using cavitation reactors filled with water and steam would address this current problem with carbonaceous fumes having insufficient reaction time with water and its ions.

The current state of the art in dehydration methods related to graphene synthesis seem to be limited to the recently reported freeze-drying dehydration of functionalized existing graphene to produce so-called “graphene aerogels” for theoretical use as electrode materials (see Hu et al., “Ultralight and Highly Compressible Graphene Aerogels,” Adv. Mat., Vol. 25, Issue 15, Apr. 18, 2013, pp. 2219-2223; Wang et al., “Manganese Oxide/Graphene Aerogel Composites as an Outstanding Supercapacitor Electrode Material,” Chemistry—A European J., Advance Publication, Dec. 10, 2013; Ye et al., “Deposition of Three-Dimensional Graphene Aerogel on Nickel Foam as a Binder-Free Supercapacitor Electrode,” ACS Appl. Mater. Interfaces, Vol. 5 (15), 2013, pp. 7112-7129; Han et al., “Ammonia solution strengthened three-dimensional macro-porous graphene aerogel,” Nanoscale, Vol. 5(21), Jun. 21, 2013, pp. 5462-5467); the only notable exception being the much earlier reported use of chemically exfoliated graphite to produce a graphene hydrogel as a precursor, subsequently freeze-dried by supercritical CO2, into a graphitic aerogel by Zhang et al, “Mechanically Strong and Highly Conductive Graphene Aerogels and its Use as Electrodes for Electromechanical Power Sources,” J. of Mater. Chem., Vol. 21, 2011, pp. 6494-6497.

These methods of the current state of the art (save the Shankman methods, supra) now stand in stark contrast to the very recently reported “sugar-blowing” (bottom-up) oxidative synthesis of graphitic foams by Wang et al., supra (originally described by Shankman as sugar dehydration/oxidation synthesis of graphene infra), that consists of synthesizing graphene from the oxidization of carbonaceous precursors. The critical difference between the Wang and Shankman methods of oxidative synthesis of graphene (aside from the Wang method's lack of vapors recovery and absence of a hydrophobic self-assembly pool), is the differing 3-D, versus 2-D, final graphene products resulting therefrom.

Hydrodynamic Cavitation Study in the Current Art

One of water's additional properties is the tremendous energy potential it possesses when subjected to inertial cavitation causing implosive collapse. The nature of implosive bubble collapse, and its corresponding heat generated, has been extensively studied (see Brennen, C. E., Cavitation and Bubble Dynamics, © 1995 Oxford University Press; Liu et al., Nuclei Population Dynamics and Cavitation, © 1995 California Institute of Technology; Didenko et al., “Hot Spot Conditions During Cavitation in Water,” J. Am. Chem. Soc., Vol. 121, No. 24, 1999, pp. 5817-5818). The temperatures within the collapsing bubble can reach 15,000° K.

The conditions within the implosions of water cavitation bubbles are seldom seen anywhere else in nature, except, oddly enough, in the bubbles emanating from the snapping claws of pistol shrimp (see Lohse et al., “Snapping shrimp make flashing bubbles,” Nature, Vol. 413, Oct. 4, 2001, pp. 477-478; Versluis et al., “How Snapping Shrimp Snap: Through Cavitating Bubbles,” Science, Vol. 289 (5487), Sep. 22, 2000, pp. 2114-2117). These unique conditions and dynamics found within imploding cavitation bubbles have been studied and characterized extensively (see Rooze, J., “Cavitation in gas-saturated liquids,” [PhD Thesis] Eindhoven University of Technology Library, Eindhoven, Netherlands, Jun. 11, 2012; Tinguely, M., “The effect of pressure gradient on the collapse of cavitation bubbles in normal and reduced gravity,” [PhD Thesis No. 5674], École Polytechnique Fédérale de Lausanne, Lausanne, Suisse, 2013; Brennen, C., Cavitation and Bubble Dynamics, © 1995, Oxford University Press).

Collision of opposing liquid streams under extreme temperatures and pressures to initiate nanoparticle nucleation, as currently practiced in the art, is caused by spontaneous dissociation of water molecules, and not via the forces and conditions found within the implosion of cavitation bubbles, as suggested by the science of the present invention.

Dendritic Ice Growth and the Formation of Graphene Snowflakes

Recently, researchers Hao et al. delivered high concentrations of oxygen to a copper foil substrate in a tube furnace, prior to producing CVD graphene by heating methane gas. The experiment showed that the surface of the Cu foil became covered in oxygen atoms, inhibiting graphene nucleation at numerous individual sites on the substrate, yet encouraging several areas of large-area graphene sheet formation instead. The compelling part of their experiments came in the resulting morphologies of the large-area graphene sheets, which were snowflake-like in shape. The resulting structures were six-sided (hexagonal symmetry) star patters with altered “dendritic” growth kinetics. Ice crystal growth is likewise hexagonal and dendritic (see Yoshizaki et al., “Precise Measurement of Dendrite Growth of Ice Crystals in Microgravity,” Microgravity Sci. Technol., Vol. 24 (4), September 2012, pp. 245-253; Kim, T. and Ming, L., “Visual Simulation of Ice Crystal Growth,” Eurographics/SIGGRAPH Symposium on Computer Animation (2003), San Diego, Calif., U.S.A.; Ellingson, L., Engaging Crystallization in Quantitative Research: An Introduction, © 2009 SAGE Publications, Inc., Thousand Oaks, Calif., U.S.A.). The pyrolysis of methane (CH4) leads to the production of (among other things), large amounts of nascent hydrogen (H+) ionic gas and (through a methanol intermediate) a certain amount of water. Under one theory, according to the disclosed science of the invention, the oxygen-saturated substrate surface (accidentally, and unbeknown to the Hao et al. team) underwent “methane oxidation” and produced a nanoscopic surface coating of water on the Cu foil (see Cho et al., “Kinetic Investigation of Oxidative Methane Pyrolysis at High CH4/O2 Ratio in a Quartz Flow Microreactor below 1073 K,” Bull. Korean Chem. Soc., Vol. 29 (8), 2008, pp. 1609-1612). As the conditions in the Hao et al. heated CVD chamber drove that water film (and ambient water vapor) to a superheated or supercritical point, the water molecules possibly organized in an “ice-like” molecular matrix (with captive carbon radicals in the center of water clathrate cages), and benzene/cyclopentane rings were formed that subsequently (under the influence of surrounding residual water vapor in the chamber) self-assembled into snowflake-like graphene sheets as they precipitated out of the hexagonal water matrix on the surface of the solid substrate (see Hao et al., “The Role of Surface Oxygen in the Growth of Large Single-Crystal Graphene on Copper,” Science, Vol. 342, Nov. 8, 2013, pp. 720-723).

This host/guest (water-cage/carbon) theorized MD model would agree with the earlier reported extremely (almost prohibitively) high single-adatom attachment energy barrier to (individual carbon atom) graphene growth (see Loginova et al., “Evidence for graphene growth by C cluster attachment,” New J. of Phy., Vol. 10, September 2008, 16 pp.). Loginova et al., supra, also suggest that graphene epitaxial growth proceeds by attachment of rare 5-carbon “clusters” to the reactive end-carbons of existing sheets (scales). Clathrate cages in solution are known to arrange themselves into a variety of host/guest and equilibrium states, including states where encapsulated phenols “separate” from solution under the influence of CO2 (see Yoon, Ji-Ho and Lee, Huen, “Clathrate phase equilibria for the water-phenol-carbon dioxide system,” AlChE J., Vol. 43, Issue 7, July 1997, pp. 1884-1893). It is theorized, in the science of the invention, that in hydrothermal synthesis conditions or other (pyrolysis) water-producing graphene synthesis conditions, carbon/water clathrate (host/guest) cages assemble into “clusters” that attach to the reactive end-carbons of graphene; whereby carbon rings merely “precipitate” out of the host water cage environment and proceed to “self-heal” (under the influence of additional surrounding water vapor) into perfect hexagons.

SUMMARY OF THE INVENTION

The invention relates to methods for synthesis of graphene and its derivatives via hydrothermal methods and combustion synthesis, dehydration and/or rapid oxidation/reduction reactions using water for the assembly and deposition of graphene films. The invention further relates to hydrodynamic cavitation reactors for synthesis of graphene and its derivatives, and the use of water in such synthesis methods.

In one embodiment, nascent synthesis and product vapors from hydrothermal synthesis, combustion synthesis and or dehydration and rapid oxidation/reduction synthesis of graphene and its derivatives are channeled through or onto aqueous solutions that comprise hydrophobic self-assembly pools for the formation of graphene and its derivatives, including graphene or GO hydrogel.

These disclosed bottom-up approaches to graphene or GO hydrogel of the present invention are superior to recently disclosed top-down approaches, attempting synthesis of highly-contiguous and uniform thermally-conductive GO gels. GO hydrogels produced by top-down methods are marred by size limitations of the individual exfoliated nano-graphitic platelets (so-called “NGPs”), that are “glued” together and not hydrophobically self-assembled into contiguous sheets (see U.S. Patent Application No. 2013/0236715 by Zhamu et al.).

In one embodiment, the liquid solution of a hydrophobic self-assembly pool is temperature manipulated (hot or cold, including inducing freeze/thaw cycles), and or otherwise manipulated by (including but not limited to, sonication, ultrasonication, application of a surfactant, application of oxidizing or reducing agents, ionizing irradiation, pH adjustment, pressurization or depressurization, heating, vibration, application of UV (or more specifically, DUV) radiation, application of sound waves or microwaves, exposure to magnetism, MASER (Microwave Amplification by Simulated Emission of Radiation), SASER (Sound Amplification by Simulated Emission of Radiation), application of an electric current or arc, temperature changes, exposure to chemical compositions including but not limited to deuterium oxide (“heavy water” or D2O), semi-heavy water (HDO), hydrogen peroxide (H2O2), glycol including but not limited to ethylene glycol or propylene glycol or combinations thereof) means to encourage formation of large-area graphene and GO sheets. In one embodiment, the liquid of the hydrophobic self-assembly pool is further processed to purify the graphene, GO or derivative product, including the use of the resulting graphene hydrogel as feedstock in another series of successive hydrothermal graphene synthesis reactions; the object thereof being to purify or functionalize the graphene or graphene derivative products.

In one embodiment, vapors from hydrothermal synthesis, combustion synthesis and or dehydration and rapid oxidation/reduction synthesis of graphene and its derivatives are collected and directed to solid substrates for the formation of graphene and its derivatives. In one embodiment, the solid substrate comprises frozen water (ice), capitalizing on water's unique properties in the synthesis of graphene sheets and water's “self-healing” effect on graphene's hexagonal ring matrix. In one embodiment, the solid substrate is selectively or entirely coated in liquid water. In one embodiment, ice is used as a solid substrate in combination with another solid substrate.

In one embodiment, the heat within the nano-environment of a collapsing cavitation water bubble is used in the nucleation of graphene by providing locally pyrolytic synthesis conditions (LPSC/LPS) that initiates graphene formation from the carbonaceous materials in the hydrothermal solution. Various embodiments of hydrothermal cavitation reactors are disclosed which encourage the formation of cavitation bubbles and their subsequent complete collapse, releasing the useful energy potential of supercritical water. Some of the revealed hydrothermal cavitation reactor designs employ channeled liquid flows and/or rotating drums to induce inertial cavitation in the reactant-containing hydrothermal solutions. In other design embodiments of hydrothermal cavitation reactors, external means are employed to induce non-inertial cavitation in the reactant-containing hydrothermal solutions. In other disclosed design embodiments of graphene synthesis reactors, carbonaceous gases are combusted with oxygen, in both micro and macro combustion environments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic and image of a common vacuum eductor (jet spray nozzle) apparatus.

FIG. 2 is a schematic image of a reversed-flow eductor, inertial cavitation-inducing apparatus.

FIG. 3 is a picture of a commercially available inertial cavitation water heater apparatus.

FIG. 4A is the inlet of a cyclonic flow inducing restrictive venturi inertial cavitation-inducing device.

FIG. 4B is the outlet of a cyclonic flow inducing restrictive venturi inertial cavitation-inducing device.

FIG. 4C is a longitudinal view of a cyclonic flow inducing restrictive venturi inertial cavitation-inducing device.

FIG. 5A is an embodiment of an “offset flow” inertial cavitation-inducing reactor embodiment.

FIG. 5B is the longitudinal view of the embodiment depicted in FIG. 5A.

FIG. 5C is another embodiment of an “offset flow” inertial cavitation-inducing reactor.

FIG. 6 is an “opposing right-angle flow” inertial cavitation-inducing reactor embodiment.

FIG. 7 is an ultrasonic transducer rod, capable of addition to a cavitation reactor.

FIG. 8 is a picture of a commercially available “dual shut-off valve.”

FIG. 9A is a schematic of a combination ultrasonic/inertial cavitation-inducing reactor.

FIG. 9B is a detailed view of the incorporated ultrasonic transducer horn within FIG. 9A.

FIG. 10 is an embodiment of a hydrodynamic cavitation reactor.

FIG. 11 is a structural diagram of methyl radical.

FIG. 12 is a representation of a single carbon atom in a guest/host relationship with a water cage.

FIG. 13 is a representation of 6 carbon/water clathrate cages aligned in a helix.

DETAILED DESCRIPTION OF THE INVENTION

It is theorized in the science of the invention that carbon radicals and nascent hydrogen ions play an important role in the disclosed synthesis methods, regardless of the means employed to generate those carbon radicals or hydrogen ions from their carbonaceous precursors. Likewise, it is theorized that water plays an equally important role in the formation of graphene from such carbon radicals. The invention relates to methods of graphene and graphene derivatives synthesis by various techniques and through various reactor designs, with subsequent purposeful collection and direction of the resulting vapors to a liquid or solid substrate whereby graphene or its derivatives are permanently deposited or recovered for other use.

Hydrothermal Synthesis of Graphene and its Derivatives

Hydrothermal synthesis routes to graphene and its derivatives are disclosed, in which polycyclic aromatic hydrocarbon (PAH) graphene sheet precursors and formed graphene scales in aqueous vapors can be purposefully collected and separated from the liquid-phase reactants in which they were formed. Additionally, the hydrothermal (wet) routes to graphene synthesis of the invention are not believed to incur the irretrievable folding/crumpling of graphene sheets, small graphene sheet size, and imperfections in the graphene hexagonal lattice structure that are commonly experienced in dry synthesis methods.

In the methods disclosed herein, a myriad of possible carbonaceous feedstock reactants can be utilized to produce graphene and graphitic materials without requiring the use of toxic, explosive, caustic, complex or expensive materials. The hydrothermal routes to graphene synthesis of the invention are believed to provide a safe, industrially-scalable, and cost effective method for synthesis of graphene and its derivatives, thereby permitting widespread global commercialization of new graphene-based technologies.

In one embodiment, methane, ethane, propane or combinations thereof can be bubbled in conjunction with hydrogen gas (H2), through alcohol solvents in a heated hydrothermal reactor chamber (see Wassei, et al., “Chemical Vapor Deposition of Graphene on Copper from Methane, Ethane and Propane: Evidence of Bilayer Selectivity,” Small, Vol. 8, Issue 9, 2012, pp. 1415-1422). The resulting vapors can then be collected and channeled, according to methods of the invention, through aqueous solutions for hydrophobic self-assembly of graphene sheets. Alternatively, the resulting vapors can be collected and directed to the surface of a solid substrate for the formation of graphene and its derivatives.

Combustion Synthesis of Graphene and its Derivatives

In one embodiment, polytetraflouroethylene (PTFE) can be heated in a mild vacuum to its thermal decomposition into certain fluorocarbon gases (i.e. tetrafluoroethylene, C2F4) and while being simultaneously reacted with silicon carbide powder in a self-sustaining exothermic reaction to produce carbon-rich vapors (see Manukyan et al., “Combustion synthesis of graphene materials,” Carbon, Vol. 62, October 2013, pp. 302-311). The resulting vapors can then collected and channeled, according to methods of the invention, through aqueous solutions for hydrophobic self-assembly of graphene sheets.

In another embodiment, methane gas can be combusted along with pure oxygen (O2) gas in a chamber designed to induce so-called “convective eddies” (reflux vortexes) that encourage the development of hot and cold zones (see Kellie et al., “Deposition of few-layered graphene in a microcombuster on copper and nickel substrates,” RSC Adv., Vol. 3, 2013, pp. 7100-7105). It is noteworthy that the oxidation of methane itself (through a methanol intermediate) produces water. The resulting exhaust vapors can then be collected and channeled, according to methods of the invention, through liquid water solutions for hydrophobic self-assembly of graphene sheets. Alternatively, the resulting vapors may be collected and directed to the surface of a solid substrate for the formation of graphene and its derivatives.

Dehydration and Rapid Oxidation/Reduction Synthesis of Graphene

In one embodiment, sugar, sodium bicarbonate and ignited alcohol or lighter fluid accelerant can be used to create a graphene/PAH-rich exhaust vapor. Other embodiments can employ ignited mixtures of nitrated linseed oil and naphthalenes. Still other embodiments can use an ignited combination of ammonium nitrate and sodium bicarbonate mixed with water/ammonium dichromate. In yet another embodiment, the aforementioned ammonium dichromate can be substituted with a flammable accelerant. The resulting exhaust vapors can then be, according to methods of the invention, collected and channeled through aqueous solutions for hydrophobic self-assembly of graphene sheets. Alternatively, the resulting vapors can then be collected and directed to the surface of a solid substrate for the formation of graphene and its derivatives.

In other illustrative embodiments, so-called “oxidative pyrolysis” of methane or other carbonaceous gases can be employed to produce the necessary graphene/PAH-rich exhaust vapors for graphene or graphene derivatives synthesis.

Hydrodynamic Cavitation Reactors for Wet Graphene Synthesis

Various embodiments of hydrothermal cavitation reactors are disclosed that encourage the formation of cavitation bubbles and their subsequent complete collapse, releasing the useful energy potential of supercritical water. In each embodiment, the vapors created can then be collected and channeled through liquid water solutions, according to methods of the invention, for hydrophobic self-assembly of graphene sheets. Alternatively, the resulting vapors can be collected and directed to the surface of a solid substrate for the formation of graphene and its derivatives.

In one embodiment, the flow directions of a common vacuum eductor apparatus (as seen in FIG. 1) can be reversed, such that the vacuum inlet is converted to a horizontal product flow discharge, and the jet spray outlet in likewise reversed into a venturi-type nozzle inlet; thus causing accelerated stream collision and cavitation bubble formation within the eductor apparatus' (former) mixing and air-entrainment chamber (as seen in FIG. 2). In this embodiment's design, the liquid streams are purposefully intended to accelerate prior to collision with each other, in a chamber or cavity providing a low-pressure area designed or employed to induce inertial cavitation bubble formation within the combined (mixed) reactant streams and resulting local “bubble harvesting” (BH) to capture the formed bubbles and maintain them (albeit temporarily) in the area of nanopartical nucleation and growth. During resulting BH and cavitation bubble collapse, these bubbles provide a nano-environment suitable for inducing nanoparticle synthesis, such as nucleating graphene (and its derivatives) formation and growth.

In another embodiment, a commercially-available rotating drum-type inertial cavitation-inducing (water heater) reactor (as seen in FIG. 3) can be employed to heat the fluids of a hydrothermal graphene synthesis system to create heated, superheated and/or supercritically heated water. In another embodiment, the pits or cavities along the surface of a rotating internal drum provide the sites for cavitation bubble formation and local BH. The resulting heated water can then be employed within the reactor chamber to nucleate graphene particle synthesis and encourage its continued growth by providing the necessary ions and radicals to accomplish graphene synthesis from carbonaceous materials heated to their point of decomposition in aqueous solution.

In another embodiment, a flow-restricting venturi device (FIG. 4C) can be employed to induce a (longitudinal vortex) cyclonic liquid flow, further comprising a “vacuum sheath” (VS) or tornadic so-called “supercavitation” event in the fluid stream; this vacuum-sheathed liquid cyclone conveniently occurring in the direction of flow of the system. In this embodiment, the entrance (inflow) orifice (FIG. 4A) is smaller than the exit (outflow) orifice (FIG. 4B), so as to create a lower pressure area at the exit as compared to the entrance. The aforementioned cyclonic flow may also be achieved by the “offset opposing flow” design embodiments (FIGS. 5A, 5B, 5C), designed to purposefully collide opposing flows at an angle to each other, rather than head on, so as to induce a circular flow about the collision within an inertial cavitation reactor chamber.

In another embodiment, an “opposing right-angle flow” inertial cavitation-inducing reactor (FIG. 6) can be employed to initiate cavitation bubbles at a right-angle juncture in the inlet flow, just prior to opposing collision of the two reactant streams. This “opposing right-angle flow” cavitation can be accomplished by reversal of the flow directions through a typical commercially available “dual shut-off valve” apparatus (as seen in FIG. 8).

In another embodiment, external non-inertial means can be employed to induce cavitation bubble formation within a reactor chamber. The means for producing such external energy for inducing cavitation in the fluid inside the reactor may comprise ultrasonic soundwave energy, delivered into the chamber by means of a transducer rod (as seen in FIG. 7) inserted or machined into the chamber.

In another embodiment, means for producing external energy for inducing non-inertial cavitation in the fluid inside the reactor may comprise radio frequency (RF) non-ionizing irradiation. In one design embodiment, the RF energy can be transmitted directly between two plates (transmitter and receiver) so as to maximize the signal delivered to the reactants in the chamber situated between them (see, for example, U.S. Patent Application No. 2009/0294300 by Kanzius, J.). The resulting heated water can then be employed within the reactor chamber to nucleate graphene particle synthesis and encourage its continued growth by providing the necessary ions and radicals to accomplish graphene synthesis from carbonaceous materials heated to their point of decomposition in aqueous solution.

In another embodiment, means for producing external energy for inducing non-inertial cavitation in the fluid inside the reactor may comprise strongly-focused laser light emissions (see Vogel et al., “Optical and acoustic investigations of the dynamics of laser-produced cavitation bubbles near a solid boundary,” J. Fluid Mech., Vol. 206, 1989, pp. 299-338). The ability of laser light emissions to induce cavitation bubble formation in liquids is known to the art (see, for example, Yan et al., “Hollow nanoparticle generation on laser-induced cavitation bubbles via bubble interface pinning, Appl. Phys. Lett., Vol 97, Issue 12, 2010; Yan, Z. and Chrisey, D. B., “Pulsed laser ablation in liquid for micro-/nanostructure generation,” J. of Photochemistry and Photobiology, Vol. 13, Issue 3, September 2012, pp. 204-223; Vogel, A. et al., “Energy density, temperature and pressure upon spherical cavitation bubble collapse compared to femtosecond and nanosecond optical breakdown,” Lasers and Elecro-Optics 2009/European Quantum Electronics Conference (CLEO-Europe, EQEC 2009) [IEEE Conference Publication], Jun. 14-19, 2009, Munich, Germany) Manipulation of bubble size and physical position is likewise possible with the use of spacial light modulator (SLM) technologies (see, for example, Quinto-su et al., “Generation of laser-induced cavitation bubbles with a digital hologram,” Optics Express, Vol. 16 (23), 2008, pp. 18964-18969). In another embodiment, the light wavelength can be in the UV spectrum to, among other things, encourage the photolytic dissociation of water into mono-atomic hydrogen ions (see, for example, Getoff, N. and Schneck, G. O., “Primary Products of Liquid Water Photolysis at 1236, 1470 and 1849 Å,” Photochem. and Photobio., Vol. 8, Issue 3, September 1968, pp. 167-178). In another embodiment, the supplied RF energy can be in the form of two or more frequencies combined (e.g. heterodyning) to stretch or break the intermolecular bonds of water, the carbonaceous feedstock materials or intermediates thereof, to produce useful radicals (see generally, the work of Puharich, A., MD (1918-1995, Dobson, N.C., U.S.), on “water decomposition” to produce nascent hydrogen; U.S. Pat. No. 4,394,230 to Puharich; and the work of Meyer, S (Grove City, Ohio, US), on “resonant electrolysis” of water molecules). The resulting heated water can then be employed within the reactor chamber to nucleate graphene particle synthesis and encourage its continued growth by providing the necessary ions and radicals to accomplish graphene synthesis from carbonaceous materials heated to their point of decomposition in aqueous solution. It is further theorized that the LPSC of the collapsing cavitation bubbles in the reactors of the present invention may provide the necessary physical conditions, when coupled with the introduction of electron irradiation (or other ionizing irradiation), UV, or specifically DUV irradiation, to produce enhanced photolytic/radiolytic dissociation of water into hydrogen ions (see, for example, Ceppatelli, M., “High-pressure photodissociation of water as a tool for hydrogen synthesis and fundamental chemistry,” Pro. Nat. Acad. Sci., Vol. 106, No. 28, Jul. 14, 2009, pp. 11454-11459). It is further theorized, in the science of the invention, that hydrogen (as synthesized and employed in various embodiments of the invention) selectively attacks the C—H bonds of the carbonaceous material feedstocks and encourages the formation of carbon radicals and the subsequent assembly of C—C bonds necessary to form graphene and its derivatives (see Tribecky, T., “Hyperthermal H2 induced C—H bond cleavage: A Novel Approach To Cross-linking Of Organic Molecules,” © 2011, University of Western Ontario—Electronic Thesis and Dissertation Repository, Paper No. 270; later published as Trebicky, T., “Cleaving C—H bonds with hydrothermal H2: facile chemistry to cross-link organic molecules under low-chemical- and energy-loads,” Green Chem., 2014 Advance Article). It is noteworthy that other highly-reactive nascent gases (such as Cl and N) may also be useful in C—H (or C═O) bond cleavage during graphene synthesis, yet these other elements appear to produce unavoidable hetero-atomic doping of the resultant graphene product surfaces.

In another embodiment, elements of non-inertial cavitation bubble production can be combined into elements of an inertial cavitation-inducing reactor (FIG. 9A). In one embodiment, miniature ultrasonic transducers (FIG. 9B) are incorporated or machined into the cavities (depressions/chambers) of a rotating cavitation-inducing drum within a cavitation reactor. The miniature ultrasonic transducer rods can be energized so as to deliver ultrasonic acoustic waves directly into the immediate area of cavitation bubble genesis and BH; an area where nanoparticle synthesis should be initiated in such embodiment. In yet another embodiment, a rotating “cheese grater” wheel—akin to a commercial food processor—can be employed (as seen in FIG. 10) to induce multiple shearing cavitation flow events.

In another embodiment, electrodes capable of producing an electrical arc discharge can be incorporated into a hydrodynamic cavitation-inducing reactor chamber. The elements of the arc discharge electrodes are designed to produce a nanoparticle inducing electrical arc in the vicinity of cavitation bubble genesis and BH. The combined forces of the electrical arc discharge and the collapsing cavitation bubbles are believed to enhance nanoparticle synthesis and growth.

In another embodiment, electron (or other ionizing) radiation, laser or DUV light can be introduced into the hydrodynamic cavitation-inducing reactor chamber, with the combined forces believed to enhance production of nascent hydrogen (or other mono-atomic) gases useful in C—H bond cleavage, C—C cross-linking and subsequent self-assembly and growth of nanoparticles, PAHs, lacey carbon ribbons, graphene/GO sheets, etc. (see, for a non-hydrodynamic, non-cavitation, simple solid substrate-using example, Matei et al., “Functional Single-layer Graphene Sheets from Aromatic Monolayers,” Adv. Mater., Vol. 25, Issue 30, Aug. 14, 2013, p. 4145; see also Angelova et al., “A Universal Scheme to Convert Aromatic Molecular Monolayers into Functional Carbon Membranes,” ACS Nano, Vol. 7, Issue 8, 2013, pp. 6489-6497).

Synthesis of Graphene and its Derivatives in the Presence of Water

It is theorized that carbon radicals play an important role in the synthesis methods of the invention, regardless of the specific method employed to generate those carbon radicals from their carbonaceous starting materials. Likewise, it is theorized that water plays an equally important role in the formation of graphene from such carbon radicals.

When considering the so-called “solute effect” in water, the uniqueness of solute hydrophobic hydration in water must be considered. It is known that methane gas can become “caged” within frozen water. The product, methane hydrate (so-called “fiery ice”) can burn aflame in the palm of the hand. Methane gas is one of the syngas species commonly produced by embodiments of the invention. Methyl radicals (CH3) are sp2-hybridized, trigonal planar carbon radicals. The fact that CH3 is already sp2-hybridized carbon plays a part in the theorized interactions between carbon and water. It is theorized that carbon atoms (as carbonyl radicals) can interact (albeit, for fractions of picoseconds at a time) with the “holes” in so-called “water cages” in liquid water. It is believed that when water is perturbed to the point of becoming superheated or supercritical (an area of water's phase diagram where a triple-point exists), portions of the water in the reaction exist in several phases (liquid, gas, solid) simultaneously, and/or water exhibits some of the molecular structure characteristics of each and all of these phases simultaneously. Water is known to surround non-polar solutes in clathrate cages (FIG. 11).

It is theorized that during graphene synthesis in the presence of water, according to the methods of the invention, carbonyl ions become surrounded in water clathrate cages in a guest/host relationship. The carbonyl ions are believed to oscillate within the “hole” in the water cage, finding brief meta-stability as pseudo-methyl radicals at each end; the carbon's available electrons briefly exchanging temporary bonds with three hydrogen atoms found like “fingers” at each of the openings of the water hole (FIG. 12). With the (fractional picoseconds) progression of time, additional water/carbon clathrate cages interact with the first, building a chain of cages that eventually folds upon itself in a helix, highly analogous to the structure of water seen in the frozen ice phase (FIG. 13). Once in this hexagonal configuration, it is theorized that the carbons then participate in bonds with each other and precipitate out of the water as benzene rings or (in the case of multiple clusters of ring cages), small groups of rings comprising PAHs.

It is unknown whether methyl radicals shed hydrogen prior to encapsulation by water, or never had them (as a carbonyl radical) before interacting directly with water, thereby sharing associations (weak bonds) with the hydrogen of surrounding water molecules (attracted to the carbon radical by its charge and their own polarity) as the cage formations grow. If carbon radicals are involved individually in the synthesis of graphene sheets, it may be to “heal” defects of departing heteroatoms from the growing deoxygenated sheets. It has been shown that carbon radicals (in vapor form) introduced to defective graphene or GO sheets in solution, contribute to their “self-healing” and repair into nearly perfect or “near pristine” graphene exhibiting a six-fold increase in electrical conductivity and >96% transparency (see Boya Dai et al., “High-quality single-layer graphene via reparative reduction of graphene oxide,” Nano Res., Vol. 4, Issue 5, May 2011, pp. 434-439). Methods of the present invention are believed to produce such carbon radicals (as nascent vapor) in solution during graphene synthesis.

It has likewise been recently revealed that “nascent hydrogen” (as generated, in situ) can contribute significantly to the ionic reduction of aqueous solutions of GO into graphene (see Pham et al., “Chemical reduction of an aqueous suspension of graphene oxide by nascent hydrogen,” J. Mater. Chem., Vol. 22, 2012, pp. 10530-10536; see also, Pham et al., Electronic Supplementary Material (ESM), J. Mater. Chem., © 2012 Royal Society of Chemistry, correcting earlier misconceptions regarding an electron-transport mechanism of chemical reduction of GO to graphene in solution via presumed adhesion of GO to the surfaces of the Zn or Al sheets; Domingues et al, “Reduction of graphene oxide films on Al foil for hybrid transparent conductive film applications,” Carbon, Vol. 63, 2013, pp. 454-459; see also Sofer et al., “Highly hydrogenated graphene via active hydrogen reduction of graphene oxide in the aqueous phase at room temperature,” Nanoscale, 2014, Advance Article).

It is especially noteworthy that elements of the present invention are believed to necessarily produce “nascent hydrogen” in situ (in aqueous solution) as part of the as-synthesized “syngas” during hydrothermal pyrolysis of carbonaceous feedstock to make graphene and its derivatives. These aforementioned recent studies serve to confirm the importance and efficacy of as-synthesized (newly formed—“nascent”) hydrogen ions in the synthesis of high-quality graphene and the deoxygenation (reduction) of any intermediate GO species into graphene. It is theorized that atomic hydrogen abstraction from reactive end-carbons of hydrogenated graphene sheets also permits hydrophobic self-assembly of graphene scales into large-area sheets. This, in contrast to coal and hydrogenous compound slurry ball milling techniques known to the art to also produce in situ molecular (H2) hydrogen, yielding amorphous hydrogenated ta-C and carbon/hydrogen clathrate species with no reported graphene or GO sheets (see U.S. Pat. No. 7,901,661 to Leuking et al.). In a related embodiment, the ball milling methods of Leuking et al., supra, may be modified by the addition of certain metallic oxide powders or nano-powders to yield novel SGANs (Surface-graphitized Abrasive Nanoparticles) for tribological and other uses. This, owing to the tendency (in some cases) of the Leuking et al., procedure to yield hydrogen trapped endohedral fullerenes; structures that theoretically could be made to comprise endohedral metallofullerenes with little additional procedural effort according to methods previously described by Shankman; namely, the addition of certain metallic oxides to the slurry.

Additionally, hydrogen ions are believed to be produced during spontaneous dissociation of water when perturbed to superheated or supercritical temperatures, according to methods of the present invention, including within the micro-environment of collapsing cavitation bubbles in aqueous solution. The importance of these mono-atomic hydrogen ions (H+) cannot be overlooked or under-emphasized when considering the MD of graphene synthesis in aqueous solution.

First-order molecular dynamics modeling at the University of Louisville (Louisville, Ky., U.S.A.) also showed that already-formed benzene rings (confined in a vacuum with hot water vapor) will cyclize into self-healing PAHs resembling graphene scales, in the absence of any metallic catalyst. The Louisville MD modeling would also appear to agree with elements of the earlier Loginova et al., modeling supra; in that carbon clusters, not individual atoms, participate in edge growth of graphene—although quite different causal conclusions were reached in these two studies. The unique water-influenced self-healing phenomenon, as seen in the University of Louisville MD modelling, is believed to be invaluable to the synthesis of both high-quality graphene and large-area graphene sheets. The absence of a metallic substrate as a framework in the aforementioned University of Louisville MD modeling suggests that water (or its surface tension) alone is capable of acting as the necessary framework/agent for graphene nucleation and growth in hydrothermal, dehydration or aqueous synthesis conditions.

Recent studies suggest that the observed University of Louisville self-healing MD mechanism may be related to the so-called “intramolecular cross-dehydrogenative coupling” (ICDC) seen in rGO treated with FeCl3 at room temperature (see Park et al., “Defect healing of reduced graphene oxide via intramolecular cross-dehydrogenative coupling,” Nanotechnology, Vol. 24, No. 18, May, 2013, Article ID. No. 185604). This Park et al. study seems to reinforce the importance and efficacy of nascent hydrogen and possibly water (through its self-ionization/autoprotolysis ions —H+, H3O+, OH—) in the synthesis, growth and self-repair of the graphene matrix.

It has been observed that residual water remaining on a substrate during graphene formation can inversely cause so-called “holey carbon” or “lacey carbon” (graphene nanoribbons) to form. This phenomenon suggests that water may also be employed on substrates to control the amount and shape of graphene deposition, enabling the hydrophobic fashioning of circuit patterns on solids. This phenomenon may be employed to serve as water or ice “etching” of graphene sheets. These disclosed “wet” methods of graphene etching of the present invention are superior to recently described “dry” methods, in that the graphene edges may be functionalized with hydrogen (—H), carbonyl (═O), carboxyl (—COOH), hydroxyl (—OH), aldehyde (R—CHO), carboxylate (RCOO—) or ester (—COOR) functional groups, or combinations thereof, in a one-step process during hydrothermal synthesis in aqueous solution according to embodiments of the invention, then introduced to water or ice “masks” or patterns on substrates to fashion circuit patterns or other intended designs or morphologies (see, in comparison, U.S. Patent Application No. 2013/0157034 by Choi et al.).

Elements of the invention reveal the special properties of water within the context of graphene synthesis. For example, it is believed that frozen water (ice) presents a novel substrate for epitaxial growth of large-area graphene sheets. Chilled water vapor can easily be applied to other solid substrates, then cooled to produce a layer of solid ice or frost upon which reactant vapor (produced according to the methods of the invention) may be deposited permanently, or temporarily to facilitate the recovery of graphene.

Additionally, it is possible to incorporate the carbonaceous precursor material (such as various polysaccharide solutions) directly into an aqueous substrate coating and once applied, thereafter dehydrate/pyrolyze the substrate coating via heating to produce a recoverable or permanent graphitic film (see, for example, U.S. Patent Application No. 2013/0209793 by Sanchez et al.).

In one embodiment, the water of the hydrophobic self-assembly pool can be temperature manipulated, including but not limited to a cycles of freezing and thawing the water, to encourage accelerated graphene formation through inducing corresponding changes in the structure and interaction of the water molecules therein. In another embodiment, audio waves, including those of acoustic levitation frequencies and strength, are used to encourage the liquid molecules in the synthesis apparatus and/or hydrophobic self-assembly pool to arrange in various geometric patterns (see generally, the phenomenon of the water-molecular hexagons of “Cymatics”; see also Su Zhao and Jörg Wallaschek, “A standing wave acoustic levitation system for large planar objects,” Archive of Applied Mechanics, Vol. 81, Issue 2, pp. 123-139, January 2011); Igor V. Smirnov, “The effect of a Specially Modified Electromagnetic Field on the Molecular Structure of Liquid Water,” Explore Issue, Vol. 13, No. 1, 2003). 

What is claimed is:
 1. A method of graphene synthesis, comprising: (a) creation of synthesis gas species from the hydrothermal heating of a carbonaceous material in a reaction chamber; (b) collection, direction and removal of the resulting vapors from the reaction chamber to a substrate; and (c) deposition of graphene on the surface of the substrate.
 2. The method of claim 1, wherein the substrate comprises water.
 3. The method of claim 2, further comprising application of sonication, ultrasonication, surfactant, oxidizing agents, reducing agents, ionizing irradiation, pH adjustment, pressurization, depressurization, heating, vibration, UV radiation, DUV radiation, sound waves, microwaves, magnetism, MASER (Microwave Amplification by Simulated Emission of Radiation), SASER (Sound Amplification by Simulated Emission of Radiation), electric current, electrical arc, heat, cooling, deuterium oxide (D₂O), semi-heavy water (HDO), hydrogen peroxide (H₂O₂), glycol or combinations thereof to the substrate.
 4. The method of claim 1, wherein the substrate comprises ice or dry ice.
 5. The method of claim 1, wherein the substrate comprises a solid surface, wherein the solid surface is coated at least in part with liquid water (H₂O), deuterium oxide (D₂O), semi-heavy water (HDO), hydrogen peroxide (H₂O₂) or combinations thereof.
 6. The method of claim 5, wherein the solid surface comprises silicon, copper, nickel, cobalt, boron, iron, gold, silver, aluminum, germanium, boron nitride, glass, ceramic, biomimetic membrane, silicon dioxide, silica, aluminum silicate, fused silica, silicon carbide, plastics, polymers, resins, epoxy, titanium, concrete, steel, asphalt, cement, nylon, graphite, diamond, amorphous carbon, h-BN, Si₃N₄, poly(2-phenylpropyl)methysiloxane (PPMS), poly(methyl methacrylate) (PMMA), polystyrene (PS), and poly(acrylonitrile-co-butadiene-co-styrene) (AB).
 7. The method of claim 1, wherein the substrate comprises a solid surface, wherein the solid surface is coated at least in part with ice.
 8. The method of claim 1, wherein the hydrothermal heating comprises heating the reaction chamber by application of a flame, an electric heating element, an electrical arc discharge or combinations thereof.
 9. The method of claim 8, wherein the reaction chamber comprises a non-inertial cavitation-inducing reactor.
 10. The method of claim 9, wherein the non-inertial cavitation-inducing reactor comprises an external energy input comprising ultrasound waves, acoustic levitation waves, pulsed laser light, radio frequency (RF) emissions, electromagnetic emissions, MASER, SASER or combinations thereof.
 11. The method of claim 9, wherein the reactor chamber comprises an inertial cavitation-inducing reactor.
 12. The method of claim 11, wherein the inertial cavitation-inducing reactor comprises a flow restricting venturi-type element, wherein the flow restricting venturi-type element comprises a curved venturi channel designed to induce cyclonic flow.
 13. The method of claim 1, wherein heating the carbonaceous material comprises pyrolysis.
 14. The method of claim 1, wherein heating the carbonaceous material comprises an oxidation/reduction chemical reaction.
 15. The method of claim 14, wherein the oxidation/reduction chemical reaction comprises dehydration of the carbonaceous material.
 16. The method of claim 15, wherein the dehydrated carbonaceous material comprises sugar.
 17. The method of claim 1, wherein the reaction chamber comprises an autoclave.
 18. The method of claim 1, wherein the synthesis gas species comprise under carbon monoxide, nascent hydrogen ions, ionic methane precursor gases and combinations thereof.
 19. A method of graphene oxide synthesis, comprising: (a) creation of synthesis gas species in the presence of an oxidizing agent from the hydrothermal heating of a carbonaceous material in a reaction chamber; (b) collection, direction and removal of the resulting vapors from the reaction chamber to a substrate; and (c) deposition of graphene oxide on the surface of the substrate.
 20. The method of claim 19, further comprising application of sonication, ultrasonication, surfactant, oxidizing agents, reducing agents, ionizing irradiation, pH adjustment, pressurization, depressurization, heating, vibration, UV radiation, DUV radiation, sound waves, microwaves, magnetism, MASER (Microwave Amplification by Simulated Emission of Radiation), SASER (Sound Amplification by Simulated Emission of Radiation), electric current, electrical arc, heat, cooling, deuterium oxide (D₂O), semi-heavy water (HDO), hydrogen peroxide (H₂O₂), glycol or combinations thereof to the substrate.
 21. A method of graphene synthesis, comprising: (a) creation of synthesis gas species from the hydrothermal heating of a carbonaceous material in a reaction chamber; and (b) collection, direction and removal of the resulting vapors from the reaction chamber to a substrate.
 22. The method of claim 21, wherein the substrate comprises water, wherein the method further comprises application of sonication, ultrasonication, surfactant, oxidizing agents, reducing agents, ionizing irradiation, pH adjustment, pressurization, depressurization, heating, vibration, UV radiation, DUV radiation, sound waves, microwaves, magnetism, MASER (Microwave Amplification by Simulated Emission of Radiation), SASER (Sound Amplification by Simulated Emission of Radiation), electric current, electrical arc, heat, cooling, deuterium oxide (D₂O), semi-heavy water (HDO), hydrogen peroxide (H₂O₂), glycol or combinations thereof to the substrate.
 23. A method of graphene oxide synthesis, comprising: (a) creation of synthesis gas species in the presence of an oxidizing agent from the hydrothermal heating of a carbonaceous material in a reaction chamber; and (b) collection, direction and removal of the resulting vapors from the reaction chamber to a substrate.
 24. The method of claim 23, wherein the substrate comprises water, wherein the method further comprises application of sonication, ultrasonication, surfactant, oxidizing agents, reducing agents, ionizing irradiation, pH adjustment, pressurization, depressurization, heating, vibration, UV radiation, DUV radiation, sound waves, microwaves, magnetism, MASER (Microwave Amplification by Simulated Emission of Radiation), SASER (Sound Amplification by Simulated Emission of Radiation), electric current, electrical arc, heat, cooling, deuterium oxide (D₂O), semi-heavy water (HDO), hydrogen peroxide (H₂O₂), glycol or combinations thereof to the substrate.
 25. A method of graphene synthesis, comprising: (a) application of a carbonaceous vapor containing C₁ to C₅ radicals to an aqueous solution; and (b) recovery of graphene from the surface of the aqueous solution.
 26. The method of claim 25, further comprising application of sonication, ultrasonication, surfactant, oxidizing agents, reducing agents, ionizing irradiation, pH adjustment, pressurization, depressurization, heating, vibration, UV radiation, DUV radiation, sound waves, microwaves, magnetism, MASER (Microwave Amplification by Simulated Emission of Radiation), SASER (Sound Amplification by Simulated Emission of Radiation), electric current, electrical arc, heat, cooling, deuterium oxide (D₂O), semi-heavy water (HDO), hydrogen peroxide (H₂O₂), glycol or combinations thereof to the aqueous solution.
 27. A method of graphene oxide synthesis, comprising: (a) application of a carbonaceous vapor containing C₁ to C₅ radicals to an aqueous solution; and (b) recovery of graphene oxide from surface of the aqueous solution.
 28. The method of claim 27, further comprising application of sonication, ultrasonication, surfactant, oxidizing agents, reducing agents, ionizing irradiation, pH adjustment, pressurization, depressurization, heating, vibration, UV radiation, DUV radiation, sound waves, microwaves, magnetism, MASER (Microwave Amplification by Simulated Emission of Radiation), SASER (Sound Amplification by Simulated Emission of Radiation), electric current, electrical arc, heat, cooling, deuterium oxide (D₂O), semi-heavy water (HDO), hydrogen peroxide (H₂O₂), glycol or combinations thereof to the aqueous solution.
 29. A method of graphene hydrogel synthesis, comprising: (a) application of a carbonaceous vapor containing C₁ to C₅ radicals to an aqueous solution; and (b) recovery of a graphene hydrogel layer from the aqueous solution.
 30. The method of claim 29, further comprising application of sonication, ultrasonication, surfactant, oxidizing agents, reducing agents, ionizing irradiation, pH adjustment, pressurization, depressurization, heating, vibration, UV radiation, DUV radiation, sound waves, microwaves, magnetism, MASER (Microwave Amplification by Simulated Emission of Radiation), SASER (Sound Amplification by Simulated Emission of Radiation), electric current, electrical arc, heat, cooling, deuterium oxide (D₂O), semi-heavy water (HDO), hydrogen peroxide (H₂O₂), glycol or combinations thereof to the aqueous solution.
 31. A method of graphene oxide hydrogel synthesis, comprising: (a) application of a carbonaceous vapor containing C₁ to C₅ radicals to an aqueous solution; and (b) recovery of a graphene oxide hydrogel layer from the aqueous solution.
 32. The method of claim 31, further comprising application of sonication, ultrasonication, surfactant, oxidizing agents, reducing agents, ionizing irradiation, pH adjustment, pressurization, depressurization, heating, vibration, UV radiation, DUV radiation, sound waves, microwaves, magnetism, MASER (Microwave Amplification by Simulated Emission of Radiation), SASER (Sound Amplification by Simulated Emission of Radiation), electric current, electrical arc, heat, cooling, deuterium oxide (D₂O), semi-heavy water (HDO), hydrogen peroxide (H₂O₂), glycol or combinations thereof to the aqueous solution.
 33. A method of composite fabrication, comprising: (a) application of a graphene hydrogel produced according to the method of claim 29, to a liquid composite mixture prior to its curing into a solid; and (b) curing the composite mixture into a solid.
 34. A method of composite fabrication, comprising: (a) application of a graphene oxide hydrogel produced according to the method of claim 31, to a liquid composite mixture prior to its curing into a solid; and (b) curing the composite mixture into a solid.
 35. A method of graphene synthesis, comprising: (a) application of a cyclic-carbon containing aqueous solution to coat a substrate that is sufficient to withstand the heat of pyrolysis of the aqueous solution; (b) pyrolysis of the aqueous solution coating on the substrate under conditions to produce graphene; and (c) recovery of graphene from the surface of the substrate.
 36. A method of surface graphitized abrasive nanoparticle synthesis, comprising: (a) ball milling of a carbonaceous material in the presence of a solvent to create a slurry; (b) addition of a metal oxide powder or a nano-powder to the slurry; and (c) recovery of surface graphitized abrasive nanoparticles from the slurry.
 37. The method of claim 36, wherein the carbonaceous material comprises solid CO₂ (dry ice), bituminous coal, peat, lignite, sub-bituminous coal, pulverized coal, nano-coal, steam coal, cannel coal, anthracite, charcoal, carbon black, activated charcoal, “activated nano-coal”, sugar char and combinations thereof.
 38. The method of claim 36, wherein the solvent comprises cyclohexane, toluene, polyphenol, benzaldehyde, benzotriazole, benzyl 1-naphthyl carbonate, benzene, ethyl benzene, styrene, benzonitrile, phenol, phthalic anhydride, phthalic acid, terephthalic acid, p-toluic acid, benzoic acid, aminobenzoic acid, benzyl chloride, isoindole, ethyl phthalyl ethyl glycolate, N-phenyl benzamine, methoxybenzoquinone, benzylacetone, benzylideneacetone, hexyl cinnamaldehyde, 4-amino-2-hydroxytoluene, 3-aminophenol, a benzoate, terpene, ethanol, methanol, isopropanol, isobutane, cyclobutane, pentane, isopentane, neopentane, cyclopentane, hexane, octane, kerosene, an ester, a ketone, an aldehyde, an ether or combinations thereof. 